Complement proteins

Definition

Complement proteins are a group of proteins that play a crucial role in the immune system by helping to identify and eliminate pathogens. These proteins work together in a cascade of reactions known as the complement system, enhancing the body's ability to fight infections and trigger inflammatory responses. Their actions include opsonization of pathogens, formation of the membrane attack complex, and promotion of inflammation, linking them closely to both innate immunity and the inflammatory response.

5 Must Know Facts For Your Next Test

1. The complement system consists of over 30 different proteins that work together to enhance immune functions.
2. There are three main pathways for activating the complement system: classical, lectin, and alternative pathways, each triggered by different stimuli.
3. Complement proteins can recruit immune cells to sites of infection through the release of chemotactic factors.
4. The activation of complement proteins leads to increased vascular permeability, allowing immune cells to access infected tissues more easily.
5. Dysregulation or deficiency of complement proteins can result in autoimmune diseases or increased susceptibility to infections.

Review Questions

• How do complement proteins enhance the body's innate immune response against pathogens?
  • Complement proteins enhance the body's innate immune response through several mechanisms. They opsonize pathogens, making them more recognizable to phagocytes like macrophages and neutrophils. Additionally, they can form the membrane attack complex (MAC) that directly lyses certain pathogens. By recruiting immune cells to the site of infection and promoting inflammation, complement proteins play an essential role in facilitating a rapid and effective immune response.
• Discuss the role of complement proteins in acute inflammation and how they contribute to the inflammatory process.
  • In acute inflammation, complement proteins play a key role by promoting vasodilation and increasing vascular permeability. When activated, they release anaphylatoxins that stimulate mast cells and basophils to release histamine, further enhancing blood flow and attracting leukocytes to the site of infection or injury. This action not only helps to contain the infection but also facilitates tissue repair. The overall effect is a more robust inflammatory response that is essential for clearing pathogens and initiating healing.
• Evaluate the implications of complement protein deficiencies on immune function and disease susceptibility.
  • Deficiencies in complement proteins can lead to significant implications for immune function and disease susceptibility. Individuals with such deficiencies may have a heightened risk for recurrent bacterial infections due to inadequate opsonization and impaired clearance of pathogens. Additionally, some deficiencies can contribute to autoimmune diseases, where the lack of regulatory control allows for unchecked immune responses against self-antigens. Understanding these deficiencies highlights the importance of complement proteins in maintaining a balanced immune response.

Related terms

Opsonization:

The process by which complement proteins coat pathogens, marking them for destruction by immune cells.

Membrane Attack Complex (MAC): A structure formed by complement proteins that creates pores in the membranes of target cells, leading to cell lysis.

Cytokines:

Signaling proteins released by immune cells that mediate and regulate immunity, inflammation, and hematopoiesis.